The present invention generally relates to contact photoelectric conversion apparatuses, and more particularly to a contact photoelectric conversion apparatus for use in converting into an electric signal images of characters, figures and the like optically read on a facsimile machine, a copying machine, an optical character reading apparatus, an electronic blackboard and the like.
Apparatuses for carrying out a photoelectric conversion by making contact with a document surface and the like are disclosed in Japanese Published Patent Applications No.54-41474 and No.55-44470, for example. In these apparatuses, a plurality of electrodes are formed at constant intervals on a transparent substrate made of glass or the like, and a film of a photoelectric conversion medium is formed on the electrodes. The side of the substrate provided with the photoelectric conversion medium makes contact with the document and the like, and the document is illuminated through the substrate so that an electrical signal in accordance with an electrical characteristic change of the photoelectric conversion medium dependent on a reflected light from the document is obtained from the electrode pairs.
However, according to these apparatuses, a photoelectric conversion part comprising the photoelectric conversion medium and the electrodes makes direct contact with the document surface and the like. For this reason, a friction is introduced when the document moves in a sub scanning direction, and the photoelectric conversion part may become damaged due to the friction. In addition, in order to obtain from the photoelectric conversion part an electrical signal in accordance with picture elements which describe an image on the document when the image is decomposed into dots, it is necessary to provide switches for selecting the electrode pairs and a driving circuit for successively driving the switches. The switches and the driving circuit must be provided independently on the substrate and be connected to the photoelectric conversion part by a plurality of conductor lines. As a result, there are problems in that the apparatus as a whole becomes bulky and a large number of assembling processes are required to produce the apparatus. As a measure of eliminating these problems, there is a method of covering the photoelectric conversion part by a wear-resistant protecting layer, providing the switches and the driving circuit in a vicinity of the photoelectric conversion part, and connecting the switches and the driving circuit to the photoelectric conversion part by a wire bonding or a tape wire or carrier. However, when such connecting means are used, a stepped portion is formed at the connecting part, and there is a problem in that a disconnection is easily formed at the connecting part upon contact with the document surface. On the other hand, when the protecting layer is formed on the photoelectric conversion part and the connecting part to such a thickness that the stepped portion will not occur, there is a problem in that the optical resolution becomes deteriorated because of the thick protecting layer.
FIG. 1 shows an example of the conventional contact photoelectric conversion apparatus. The photoelectric conversion apparatus comprises a substrate 11, a photoelectric conversion part 12, a driving circuit 13, and a wire bonding 14 which connects the photoelectric conversion part 12 and the driving circuit 13. In this case, a distance d between a top surface of the substrate 11 and an upper end of the wire bonding 14, that is, a height difference at the connecting part, is 100 .lambda.m or over even at the minimum, and the distance d is normally in the order of 400 .mu.m.
When a protecting layer is formed on the connecting part so as to prevent a disconnection at the connecting part upon direct contact with the document surface, the protecting layer becomes thick and a distance between a top surface of the protecting layer and a top surface of the photoelectric conversion part 12 becomes 100 .mu.m or over even at the minimum. Accordingly, when the protecting layer is formed on the photoelectric conversion part 12 so as to eliminate the height difference between the top surface of the protecting layer and the top surface of the photoelectric conversion part 12, the protecting layer on the photoelectric conversion part 12 becomes thick and the optical resolution deteriorates. According to experiments conducted by the present inventor, it has been confirmed that the optical resolution greatly deteriorates when the thickness of the protecting layer on the photoelectric conversion part 12 is 100 .mu.m or over, as shown in FIG. 2, MTF denotes the modulation transfer function.
The problems described before are eliminated if the photoelectric conversion part and the connecting part were formed on the substrate at positions sufficiently separated from each other, by a minimum of 5 mm and preferably 10 mm or over. But in this case, there is a problem in that the apparatus as a whole becomes bulky because of the large substrate area that would be required. In addition, when the substrate area increases, the cost of the materials used for the apparatus increases due to the necessity to use more substrate material and materials related to lithography used when forming patterns on the substrate. Moreover, during a process of forming a thin film in a vacuum apparatus, for example, the processing quantity per batch decreases. Therefore, there is also a problem in that the apparatus becomes expensive.